When a filament yarn, particularly a thermoplastic synthetic filament yarn, is wound on a bobbin to form a yarn package by means of a conventional ring twister or a conventional draw-twister, a twist ring is vertically reciprocated along a bobbin inserted onto a rotatable projecting spindle and the traverse stroke thereof or the winding position thereof is successively changed from the initial winding condition to the final winding condition (this is called a building motion or traverse motion) so that a package is formed on the bobbin.
Traverse apparatus disclosed in prior references, for example, Japanese Patent Publication No. 21942/66, Japanese Utility Model Publication No. 42181/77 and U.S. Pat. No. 3,695,529, have been utilized as apparatus for winding a filament yarn into a package. Consequently, filament yarns have been wound into packages in accordance with various kinds of traverse methods, such as warp winding, parallel winding or wandering winding.
A filament yarn, especially a synthetic filament yarn, wound in accordance with any one of such winding methods, however, has a defect in that, when it is utilized in knitted fabrics or woven fabrics, especially as a warp yarn of woven fabrics, bright specks may frequently occur. It has been known that the bright specks are caused by nonuniformity of yarn quality due to the change in quality of a filament yarn wound on a bobbin. It has also been known that nonuniformities of yarn are generated between an end portion and a central portion of the package, and between an inner, an intermediate and an outer portion of the package, and especially, that a filament yarn located at the inner portion has a large amount of nonuniformity between the end portion and the central portion thereof. This is because, in the filament yarn located at the inner portion adjacent to the bobbin, the stress relaxation does not occur freely since the filament yarn at the inner portion is prevented from contraction by the bobbin, and the stress relaxation in the filament yarn located at the outer or the end portion of the package is small since the compressive force from the outside is small. On the other hand, the filament yarn located at the central and intermediate portion is compressed strongly from the outside thereof, and therefore, a large amount of stress relaxation is caused. Consequently, it has been concluded that, in the filament yarn located at the intermediate portion, the difference in the stress relaxations between in the yarns located at the end portion and the central portion is very large and that, as a result, nonuniformity of yarn quality which causes bright specks is generated.
A winding method is known wherein a yarn is wound around a bobbin by utilizing a winding pattern wherein the traverse stroke is successively increased from the commencement of the winding to the completion of the winding (see U.S. Pat. No. 2,980,362). The term "winding pattern" means a shape surrounded by envelopes of the uppermost and lowermost traverse strokes when time is plotted on an abscissa and the traverse stroke is plotted on an ordinate. However, if a yarn package is wound on a bobbin by utilizing such a winding pattern, the weight of the wound package must be very small, or the package cannot be fully wound on the bobbin.